Vacuum cleaners typically comprise a downwardly directed dirty-air inlet arranged in the cleaner head or a floor tool, through which dirty air is sucked, by means of a motor-driven fan, into dirt and dust separation apparatus. An agitator, such as a brush bar, may be arranged in the mouth of the dirty air inlet so as to agitate the fibres of a carpet over which the vacuum cleaner is passed. The agitator helps to release dirt and dust trapped in the carpet. The agitator is normally driven by means of a motor via a gear or belt transmission system. The motor may be a dedicated agitator motor or a turbine, or may be the vacuum motor that powers the cleaner.
In the case that the vacuum motor is employed, a system of belts and pulleys may be employed between the motor and the agitator to transmit torque to the agitator. The relative diameters of the pulleys are arranged so as to reduce the rotational speed of the motor to a suitable rotational speed for the agitator.
A problem which may be encountered with this system is that some of the belts are driven at high speeds, which causes wear. Over time, these belts deteriorate and need periodical replacement.
It is desirable to be able to bring the agitator into and out of operation. In the case that the agitator is driven by the vacuum motor, a clutch mechanism may be provided. When the clutch is engaged, torque generated by the motor is applied to the agitator. When the clutch is disengaged, torque is not applied to the agitator.
A further problem which may be encountered with vacuum cleaners having an agitator is that, on occasion, the agitator may become jammed by becoming entangled with objects on the floor surface, for example, or by being pressed hard into the floor. It has been proposed to provide means for limiting the torque applied to the jammed agitator by, for example, causing a drive belt to slip. However, this may cause further deterioration of the belt, thereby reducing its lifetime. This is a nuisance to the user.